The field of invention relates generally to nano-fabrication of structures. More particularly, the present invention is directed to a method of providing desirable wetting and release characteristics between a mold and a polymerizable composition suitable for use in imprint lithographic processes.
Nano-scale fabrication involves the fabrication of very small structures, e.g., having features on the order of one nano-meter or more. A promising process for use in nano-scale fabrication is known as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as U.S. Pat. No. 6,980,259; U.S. Patent Application Publication No. 2004/065252; and U.S. Pat. No. 6,936,194, all of which are assigned to the assignee of the present invention.
Referring to FIG. 1, the basic concept behind imprint lithography is forming a relief pattern on a substrate that may function as, inter alia, an etching mask so that a pattern may be formed into the substrate that corresponds to the relief pattern. A system 10 employed to form the relief pattern includes a stage 11 upon which a substrate 12 is supported. A template 14 has a mold 16 with a patterning surface 18 thereon. Patterning surface 18 may be substantially smooth and/or planar, or may be patterned so that one or more recesses are formed therein. Template 14 is coupled to an imprint head 20 to facilitate movement of template 14. A fluid dispense system 22 is coupled to be selectively placed in fluid communication with substrate 12 so as to deposit polymerizable material 24 thereon. A source 26 of energy 28 is coupled to direct energy 28 along a path 30. Imprint head 20 and stage 11 are configured to arrange mold 16 and substrate 12, respectively, to be in superimposition, and is disposed in path 30. Either imprint head 20, stage 11, or both vary a distance between mold 16 and substrate 12 to define a desired volume therebetween that is filled by polymerizable material 24.
Typically, polymerizable material 24 is disposed upon substrate 12 before the desired volume is defined between mold 16 and substrate 12. However, polymerizable material 24 may fill the volume after the desired volume has been obtained. After the desired volume is filled with polymerizable material 24, source 26 produces energy 28, which causes polymerizable material 24 to solidify and/or cross-link, forming polymeric material conforming to the shape of the substrate surface 24 and mold surface 18. Control of this process is regulated by processor 32 that is in data communication with stage 11, imprint head 20, fluid dispense system 22, and source 26, operating on a computer readable program stored in memory 34.
An important characteristic with accurately forming the pattern in the polymerizable material is to reduce, if not prevent, adhesion to the mold of the polymeric material, while ensuring suitable adhesion to the substrate. This is referred to as preferential release and adhesion properties. In this manner, the pattern recorded in the polymeric material is not distorted during separation of the mold therefrom. Prior art attempts to improve the release characteristics employ a release layer on the surface of the mold. The release layer is typically hydrophobic and/or has low surface energy. The release layer adheres to the mold. Providing the release layer improves release characteristics by minimizing distortions in the pattern recorded into the polymeric material that are attributable to mold separation. This type of release layer is referred to, for purposes of the present discussion, as an a priori release layer, i.e., a release layer that is solidified to the mold.
Another prior art attempt to improve release properties is described by Bender et al. in “Multiple Imprinting in UV-based Nanoimprint Lithography: Related Material Issues,” Microeletronic Engineering, 61-62 (2002), pp. 407-413. Specifically, Bender et al. employ a mold having an a priori release layer in conjunction with a fluorine-treated UV curable material. To that end, a UV curable layer is applied to a substrate by spin-coating a 200 cPs UV curable fluid to form a UV curable layer. The UV curable layer is enriched with fluorine groups to improve the release properties.
A drawback with the release layers of the prior art is that the same usually increases the time required to wet a surface, thereby reducing the overall throughput of the process. This, it is believed, results from the hydrophobicity of the release layers. Specifically, the hydrophobicity is inversely related to the work required to achieve release and directly related to the time required to wet a surface. Thus, there is a conflict between the wetting characteristics and the release characteristics desired for imprint lithographic processes.
There is a need, therefore, to improve the preferential release and adhesion properties of a mold employed in imprint lithography processes.